Pseudogout (calcium pyrophosphate dihydrate crystal deposition disease) is a disorder caused by deposits of calcium pyrophosphate dihydrate crystals in and outside the fluid of the joints, leading to intermittent attacks of painful joint inflammation.
Pseudogout usually occurs in older people and affects men and women equally.
The reason that calcium pyrophosphate dihydrate crystals form in some people is unknown. It may occur in people who have had a joint injury (including surgery), and in people who have other diseases, such as gout (see Gout and Pseudogout: Gout), accumulations of protein in various organs and tissues (amyloidosis), a severely underactive thyroid gland (myxedema), an abnormally high calcium level in the blood caused by a high level of parathyroid hormone (hyperparathyroidism), an abnormally high iron level in the tissues (hemochromatosis), or an abnormally low magnesium level in the blood (hypomagnesemia). However, most people with pseudogout have none of these conditions. The disorder can be hereditary. The calcium crystals frequently occur in joints affected by osteoarthritis (see Joint Disorders).
Symptoms vary widely. Some people have attacks of painful joint inflammation (arthritis), usually in the knees, wrists, or other relatively large joints. Other people have lingering, chronic pain and stiffness in joints of the arms and legs, which may be similar to rheumatoid arthritis or osteoarthritis. Sudden painful (acute) attacks are usually less severe than those of gout, but as in gout, attacks in pseudogout can cause fever. Some people have no pain between attacks, and some have no pain at any time, despite large deposits of crystals. Unlike in gout, people with pseudogout do not develop hard lumps of crystals (tophi).
Doctors suspect the diagnosis in older people with arthritis, particularly when joints are swollen, warm, and painful. Doctors confirm the diagnosis by removing a fluid sample from an inflamed joint through a needle (joint aspiration). Calcium pyrophosphate dihydrate crystals are found in the joint fluid. They can be distinguished from uric acid crystals (which cause gout) using a special polarized light microscope. Masses of calcium pyrophosphate crystals, unlike uric acid crystals, can be seen on an x-ray.
Often, the inflamed joints heal without any residual problems. However, in many people, chronic arthritis and permanent joint damage can occur, with some joints so severely destroyed that they can be confused with neurogenic arthropathy (Charcot joints—see Joint Disorders: Neurogenic Arthropathy (Charcot Joints)).
Usually, treatment can stop acute attacks and prevent new attacks but cannot reverse changes in already damaged joints. Most often, nonsteroidal anti-inflammatory drugs (NSAIDs—see Pain: Nonsteroidal Anti-Inflammatory Drugs) are used to promptly stop the pain and inflammation of acute attacks. Colchicine can be given by mouth in daily low doses to limit the number of attacks. Sometimes, excess joint fluid is drained and a corticosteroid suspension is injected into the joint to rapidly reduce the inflammation and pain.
No specific effective long-term treatment is available. However, physical therapy (such as muscle-strengthening and range-of-motion exercises) may be helpful to maintain joint function.
Last full review/revision May 2013 by Lawrence M. Ryan, MD